Labour MP Tom Watson has lashed out at newspaper publishers and editors by accusing them of “fixing” legislation that affected them and operating “like a mafia.”

In delivering the second annual Leveson lecture for the Hacked Off campaign, he said: “They [the press] have operated like a mafia, intimidating here, bribing there, terminating careers when it suits them and rewarding their most loyal toadies.

“For years, they could ‘fix’ any legislation that affected them, in a way that no other industry could. But it didn’t stop there. Their influence was so great that it became impossible to know who was really running the country.”

Watson referred to the new regulator created by publishers, the Independent Press Standards Organisation (Ipso) in succession to the Press Complaints Commission, as “business as usual”.

Describing the publishers as a “little group of greedy, cruel men”, he said they had “raised two fingers to Leveson, to parliament, to their victims and to the public.

“They don’t want fairness, they don’t want change. No catalogue of the wrongdoing they have overseen would be long enough to shame them. They want business as usual, so they want Ipso.”

He said parliament must deal with the “unfinished business” of press regulation and called on Labour, and the other parties, to “accept the John Major challenge” – to make general election manifesto commitments to reform of the press.

He suggested that “the public will judge them [politicians] harshly” if they fail to commit to implementing Leveson in their manifestos.

His call was supported by Joan Smith, Hacked Off’s executive director, who said: “Two years on from the Leveson report, it is vital that we again draw attention to the unfinished business of reform of press regulation.”

Watson also wants Sir Brian Leveson to reconvene his inquiry, as originally agreed in parliament, to consider the role of the police.

He said: “It is vital that Leveson 2 does begin as soon as the criminal cases are over … because the papers and others claim the police somehow got off lightly in Leveson [part 1].”